1. Field of the Invention
The present invention relates to an injection molding machine with a core drive apparatus for driving a movable core of a mold used in molding a product having an undercut portion, and more particularly, to a core drive apparatus capable of being easily connected with a movable core and accurately driving the movable core.
2. Description of the Related Art
In injection molding operation, a molding cavity of a mold is filled with a molten resin, and the filler resin is cooled and solidified in the molding cavity, whereupon a product is obtained. If the shape of the product is simple, the product can be taken out of the mold by only separating a movable-side mold half from a stationary-side mold half and pushing the product out of the movable-side mold half. If the product has an undercut portion, thread portion, or hollow portion, however, it sometimes cannot be taken out of the mold. For example, the movable-side mold half may be prevented from moving away from the stationary-side mold half by the undercut portion of the product, or the product may be prevented from being pushed out of the movable-side mold half, due to the engagement between the thread portion or hollow portion of the product and its corresponding portion of the movable-side mold half.
In molding the product of this type, therefore, a mold is used in which a mold portion (movable core) corresponding to the undercut portion or the like of the product is movable with respect to the remaining portion of the mold. The movable core is separated from the movable- and stationary-side mold halves by being driven by means of a mechanical core drive mechanism, such as an angular pin, angular cam, etc., or a fluid-operated core drive mechanism, such as a hydraulic cylinder apparatus or pneumatic motor, whereby the movable-side mold half can be moved away from the stationary-side mold half, or the product can be released from the mold.
In molding a product which has indentations (undercut portion) on its outer peripheral surface, for example, a mold is used which includes a slide core attached to a movable-side mold half so as to be movable in a direction perpendicular to the mold opening and closing direction and used to mold the indentations of the product. In this case, a molten resin is filled into a molding cavity and solidified in a manner such that the slide core is locked in a molding position by means of a locking block. Subsequently, the movable-side mold half is moved away from the stationary-side mold half after the slide core is unlocked, whereby the slide core is disengaged from the product along an angular pin, which extends at an angle to the mold opening and closing direction and has one end fixed to the stationary-side mold half, so that the product can be pushed out of the mold.
Although the mechanical core drive apparatus of this type has a simple construction, it can only linearly move the movable core. The movable core must be rotated, on the other hand, in drawing the product out of the movable core having a thread portion corresponding to the thread portion of the product. Accordingly, the mechanical core drive apparatus is not fit for the molding of the product having the thread portion.
The fluid-operated core drive apparatus, which requires a working fluid source and a tube for connecting the working fluid source and the core drive apparatus, is complicated in construction. Thus, the connection between the movable core and the core drive apparatus costs much labor, so that attaching the mold to the injection molding machine takes much time, resulting in lower operating efficiency. Further, a control device for controlling the drive of the fluid-operated core drive apparatus is provided separately from a control device which is conventionally provided for the injection molding machine in order to control the operations of an injection unit, mold clamping unit, product takeout unit, etc. Depending on the core drive apparatus which operates under the control of the former control device, therefore, the operating timing, operating speed, or operating stroke of the movable core sometimes cannot be accurately controlled in association with molding cycles executed by means of the various units under the control of the letter control device.